Many materials based on molecules, biomolecules, polymers, gels, living tissue, etc are so-called soft materials. Such soft materials have found its way into electronic devices known as molecular electronic devices. Commercial applications of such molecular electronic devices are in the form of thin-films in displays, organic light emitting diodes, or bendable devices. Despite these applications, many questions regarding the details of the mechanisms of charge transport across molecules and the molecule-electrode interfaces remain unanswered. Molecular electronic devices that are based on single molecules, or self-assembled monolayers (SAMs), are potentially good test-beds to study charge transport across molecules and the molecule-electrode interfaces at the nano-scale. The fabrication of such devices is challenging because of the difficulty to form macroscopic-scale electrical contacts to the molecules in non-invasive ways, with high reproducibility, and minimum numbers of defects.
To perform accurate physical-organic studies of charge transport across SAM-based tunneling junctions, it is essential to develop fabrication techniques that have ideally no impact to the chemical structure, or surpamolecular structure of the SAMs, and produce the same data across different operators. In reality, experimental approaches produce devices with defects, e.g., induced by surface roughness of the electrodes, phase domain boundaries of the SAMs, or variations in the details of top-electrode or the conditions of the fabrication process, whose electrical characteristics follow certain distributions. The number of the defects, and the distributions they follow, in these junctions depend on a large number of factors which directly depends on the users. Although the fabrication of the top-electrode received by far the most attention, the quality of the junctions depends equally important on the details of the fabrication of the bottom-electrode (the surface roughness depend on the pre-treatment of the target surface, deposition rate of the metal, base-pressure and cleanliness of the deposition chamber, quality of the metal in the crucible), SAM formation (the purity of the thiol-precursor, quality of the solvent, SAM-formation time, rinsing procedures). Some of these factors are perhaps easier to control, and to capture in the experimental section of a scientific report, than others, but all these factors complicate to generate molecular electronics reproducibly.
Further, these soft materials cannot withstand the rough fabrication methods that are need to form electrical contact to them using conventional deposition techniques (metals melt at temperature far above the decomposition temperature of soft-materials, these materials can also not withstand the high vacuum conditions).
Electronic devices based on organic materials already find commercial applications in the form of thin-films in displays, organic light emitting diodes, or bendable devices. The conventional method of forming the electrical contact between the electrode and the organic materials by depositing metal vapor or solid metals on top of these materials typically damages the molecules and limited the yield and the performance of the devices. It is essential to develop new fabrication techniques that have minimal impact to not only the chemical structure, but also to the supramolecular structure of these soft matter.